<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>计数器</title>
    <!-- 开发环境版本 -->
    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
    <style>
      span {
        border: 1px solid;
      }
    </style>
  </head>
  <body>
    <div id="app">
      <div class="num">
        <button @click="sub">-</button>
        <span>{{num}}</span>
        <button @click="add">+</button>
      </div>
    </div>
    <script>
      var app = new Vue({
        el: "#app",
        data: {
          num: 1,
        },
        methods: {
          sub: function () {
            if (this.num > 0) {
              this.num--;
            } else {
              alert("别减了哥");
            }
          },
          add: function () {
            if (this.num < 10) {
              this.num++;
            } else {
              alert("哥不能再大了");
            }
          },
        },
      });
    </script>
  </body>
</html>
